1. Field of the Invention
The present invention relates to a dielectric ceramic composition used as a dielectric layer of an electronic device, such as a multilayer ceramic capacitor, the production method and an electronic device having the dielectric ceramic composition as a dielectric layer.
2. Description of the Related Art
a multilayer ceramic capacitor as an example of an electronic device is produced, for example, by printing a predetermined pattern of an internal electrode on a ceramic green sheet comprising a predetermined ceramic composition, stacking them by two or more to form one body, and co-firing a green chip obtained thereby. Since the internal electrode layer of the multilayer ceramic capacitor is fired to be one body with a ceramic dielectric, it is necessary to select a material of not reacting with the ceramic dielectric. Therefore, as a material to compose the internal electrode layer, noble metals, such as platinum and palladium, had to be used in the related art.
However, in recent years, a dielectric ceramic composition capable of using inexpensive base metals, such as nickel and copper, has been developed and a wide reduction of the cost has been realized.
Also, in recent years, demands for downsizing of electronic devices have become high as the electronic circuit becomes high in density, and multilayer ceramic capacitors have rapidly become more compact and larger in capacity. To make the multilayer ceramic capacitor more compact and larger in capacity, a method of making the dielectric layer thinner and a method of increasing a specific permittivity of a dielectric ceramic composition included in the dielectric layer, etc. have been generally used. However, when the dielectric layer is made thin, an electric field imposed on the dielectric layer becomes strong when applying a direct current voltage, so that there has been a problem that change of the specific permittivity over time, that is, change of the capacity over time becomes remarkably large.
To improve the capacity under a direct current electric field over time, a method of using dielectric particles having a small average particle diameter as dielectric particles included in the dielectric layer has been proposed (for example, the Japanese Unexamined Patent Publication No. 8-124785). The Japanese Unexamined Patent Publication No. 8-124785 discloses a dielectric ceramic composition having a specific composition, wherein an average particle diameter of dielectric particles is 0.45 μm or smaller. However, the dielectric ceramic composition disclosed in this article has too low specific permittivity, so that it is difficult to attain downsizing and a larger capacity.